CI: Fix use of glob to find baseline screenshot of evergreen browser https://github.com/mathquill/mathquill/commit/9aca1a02a6b8ccc2a41904cc57713847401b3cbb#commitcomment-20870854

diff --git a/circle.yml b/circle.yml
index 3cdc574..e68e1fc 100644
--- a/circle.yml
+++ b/circle.yml

@@ -212,7 +212,7 @@
       for file in $(ls *.png); do
         # if evergreen browser, browser version of previous screenshot may not match,
         # so replace previous browser version with glob
-        baseline=baseline/"$(sh -c "ls $(echo $file | sed 's/[^_]*_(evergreen)/*/')")"
+        baseline="$(sh -c "ls \"baseline/$(echo $file | sed 's/[^_]*_(evergreen)/*/')\"")"
         echo "Number of different pixels from baseline in $file:"
         compare -metric AE $baseline $file ${file/%.png/_DIFF.png}
       done